JPWO2014136614A1 - Method for forming semiconductor thin film - Google Patents

Abstract

A method for forming a semiconductor thin film according to the present disclosure includes forming a thin film containing any one of Ge, Si, and a SiGe mixture and Sn at 0.1 at% or more and 20 at% or less on a substrate. Irradiating the thin film with pulsed laser light.

Description

  The present disclosure relates to a method for forming a semiconductor thin film.

  Semiconductor thin films are used not only for transistor channel materials, which are basic elements of large-scale integrated circuits and flat panel displays, but also for a large number of electrical and electronic devices ranging from light absorption materials for solar cells. At present, the main material of these electric and electronic devices is a group IV semiconductor, and silicon (Si) is the mainstream among them. Until now, in semiconductors using Si or the like, device performance has been improved by improving the device structure (miniaturization, surface texture, etc.). However, it is approaching the limit values depending on the physical properties (carrier mobility, light absorption coefficient) of Si itself, and material development of semiconductor materials other than Si has begun actively. Examples include III-V semiconductors, oxide semiconductors, organic semiconductors, etc., but from the viewpoint of reliability of transistor and solar cell operation (P-type / N-type doping control, threshold voltage control, etc.). As a semiconductor material, Si still has an overwhelming advantage.

  Based on the above background, germanium (Ge), which is the same group IV element as Si, has recently been regarded as a promising new material to replace Si. Ge has the characteristics that it has higher carrier (electron and hole) mobility than Si and has a large light absorption coefficient. For this reason, demonstration experiments regarding high-speed operation of transistors using Ge as a channel material have been actively conducted (for example, Non-Patent Documents 1 and 2).

  On the other hand, addition of tin (Sn), which is the same group IV element as Si and Ge, is also under investigation. According to the theoretical calculation disclosed in Non-Patent Document 3, by adding Sn, a dramatic improvement in physical property values (carrier mobility, light absorption coefficient, etc.) of the group IV semiconductor is expected. In fact, the inventors have found that by adding Sn into Ge, it is possible to suppress the point defect density, which has been a problem peculiar to Ge (Non-Patent Document 4).

In order to take full advantage of the characteristics of Si _x Ge _y Sn _11-xy semiconductors composed of such group IV elements (Si, Ge, Sn), an amorphous substrate (glass, plastic, etc.) Crystal growth at is also important. In Non-Patent Document 5, by using the melt growth method in a thermal equilibrium state, 0.1 to 0.4% in the lateral direction on a Si substrate coated with an amorphous (silicon dioxide (SiO ₂ )) film. It is disclosed that the growth of a GeSn thin film having a Sn concentration gradient of / μm% has been realized.

  In addition, in order to form a film on a glass substrate having low heat resistance, a low temperature process, specifically, crystal growth at a temperature of 500 ° C. or less is also being studied. Non-Patent Document 6 discloses that by adding 0.2% to 2% of Sn to a Ge thin film, the solid phase growth temperature can be lowered as compared with the case where Sn is not added. . Non-Patent Document 7 discloses that heat treatment (metal-induced solid phase growth) using a eutectic reaction in a non-thermal equilibrium state of Sn—Ge can be performed to lower the crystallization process temperature to about 200 ° C. Has been.

JP 2007-109943 A

K. Morii et al. , IEEE Electron Device Letters Vol. 31, p. 1092 (2010). C. H. Lee et al. IEDM Technical Digest, San Francisco, USA, 2010, p. 417. P. Moontragoon et al. , Semiconductor Science and Technology, Vol. 22, no. 7, p. 742 (2007). O. Nakatsuka et al. , Japanese Journal of Applied Physics, Vol. 49, No. 4, p. 04DA10 (2010). M. Kurosawa et al. , Applied Physics Letters, Vol. 101, no. 9, p. 091905 (2012). W. Takeuchi et al. , Extended Abstracts of the 2012 International Conference on Solid State Devices and Materials, Kyoto, 2012, p. 739. Kurosawa et al., 73rd Japan Society of Applied Physics Academic Lecture Proceedings, Ehime, 2012, p. 13-146.

Overview

  However, since the crystallinity of a semiconductor thin film and the heat treatment temperature are generally in a trade-off relationship, it is extremely difficult to obtain a high quality semiconductor thin film by film formation at a low temperature. For example, in the method disclosed in Non-Patent Document 5, a high-quality group IV semiconductor crystal can be obtained, but heat treatment at a temperature at which Ge is melted (938 ° C.) or higher is required. It cannot be formed on a resin substrate such as a substrate, a PEN (Polyethylene naphthalate) substrate, a PET (Polyethylene terephthalate) substrate, a PI (polyimide) substrate, or a PC (polycarbonate) substrate.

  In the methods disclosed in Non-Patent Documents 6 and 7, since the film formation temperature is a relatively low temperature process of 200 ° C. to 500 ° C., film formation on a glass substrate or a resin substrate is possible. It is extremely difficult to obtain a high-quality semiconductor thin film as disclosed in Patent Document 5.

  In order to solve such problems, there is a need for a method for forming a semiconductor thin film containing a mixture of Ge, Si, and SiGe having high carrier mobility and excellent surface flatness. There is a need for a method of forming a semiconductor thin film that can be formed on a substrate having low heat resistance such as a glass substrate or a plastic substrate.

  The present disclosure includes forming a thin film containing any one of Ge, Si, and a SiGe mixture and Sn of 0.1 at% or more and 20 at% or less on a substrate, and applying a pulse laser to the thin film. Irradiating with light.

Several embodiments of the present disclosure are described below by way of example only and with reference to the accompanying drawings.
Process drawing of method for forming semiconductor thin film of present disclosure Structural diagram of a laser beam irradiation apparatus for forming a semiconductor thin film of the present disclosure in a pure water atmosphere Correlation diagram between laser fluence and crystallization rate Correlation diagram between laser fluence and crystal grain size Correlation diagram between laser fluence and Sn composition in polycrystal Correlation diagram of Sn composition and laser fluence and crystal state in Ge thin film (in air) Correlation diagram between composition and laser fluence of Sn contained in Ge thin film and crystal state (in pure water atmosphere)

Embodiment

  Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. Embodiment described below shows an example of this indication and does not limit the contents of this indication. In addition, all the configurations and operations described in the embodiments are not necessarily essential as the configurations and operations of the present disclosure. In addition, the same referential mark is attached | subjected to the same component and the overlapping description is abbreviate | omitted.

(Method for forming semiconductor thin film)
A method for forming a semiconductor thin film in the present embodiment will be described with reference to FIG.

  First, as shown in FIG. 1A, a silicon oxide film 11 is formed on a substrate 10 by CVD (Chemical Vapor Deposition) or the like, and Ge to which Sn is added on the silicon oxide film 11 is formed. A thin film 20a is formed. Specifically, a silicon thin film 20a on which a silicon oxide film 11 is formed on a silicon substrate to be the substrate 10 is chemically cleaned and then placed in a vacuum deposition apparatus so that the substrate temperature is set to room temperature and Sn is added to the Ge thin film 20a. Is deposited. The film forming method may be sputtering, chemical vapor deposition, or the like in addition to vacuum deposition. In the above description, a silicon substrate is used as the substrate 10, but the substrate 10 may be a resin substrate such as a glass substrate, a PEN substrate, a PET substrate, a PI substrate, or a PC substrate. Further, instead of the silicon oxide film 11, a silicon nitride (SiN) film, a laminated film of a silicon oxide film and a silicon nitride film, or the like may be used.

  The Ge thin film 20a to which Sn is added is formed in an amorphous state because the film is formed at a room temperature. The Ge thin film 20a to which Sn is added, preferably has a Sn composition of 0.1 at% or more and 20 at% or less. Moreover, the film thickness of the Ge thin film 20a to which Sn is added is preferably 10 nm or more and 1 μm or less, and more preferably 20 nm or more and 200 nm or less. In the present embodiment, the thickness of the formed Ge thin film 20a to which Sn is added is about 50 nm.

Next, as shown in FIG. 1B, the Ge thin film 20a to which Sn is added is pulsed with laser light. That is, pulse laser light is irradiated. Specifically, a substrate 10 on which the silicon oxide film 11 is formed and a Ge thin film 20a to which Sn is added is formed in a laser irradiation apparatus, and laser light is irradiated in pulses. As described above, when the Ge thin film 20a doped with Sn is irradiated with a pulsed laser beam, the Ge thin film 20a doped with Sn is instantaneously melted and then cooled, as shown in FIG. As shown, a Ge thin film 20p crystallized and doped with Sn is formed. The crystal state of the Ge thin film 20p doped with Sn thus crystallized is a polycrystalline state, and becomes a semiconductor thin film. In the present embodiment, the beam shape of the laser beam irradiated with pulses is about 360 × 850 μm ² , and the pulse width of the irradiated laser beams is about 55 ns.

  In order to increase the crystal grain size in the Ge thin film 20p to which Sn is added, the Ge thin film 20a to which Sn is added when the Ge thin film 20a to which Sn is added is irradiated with a pulsed laser beam. It is preferable that it is more than melting | fusing point. In addition, when the laser beam is pulse-irradiated, the atmosphere in which the substrate 10 on which the Ge thin film 20a to which Sn is added is formed is installed may be an air atmosphere, and an inert gas (nitrogen, argon, or the like) ) Atmosphere, in a vacuum, or a pure water atmosphere (pure water).

(Pulse irradiation of laser light in pure water atmosphere)
Next, a method of irradiating laser light to the Ge thin film 20a added with Sn formed on the substrate 10 or the like in a pure water atmosphere will be described with reference to FIG. In the pure water atmosphere, the laser beam irradiation apparatus shown in FIG. 2 is used when irradiating the Ge thin film 20a formed on the substrate 10 or the like to which the Sn thin film is pulsed with the laser beam. Specifically, the substrate 10 on which the Ge thin film 20a to which Sn is added is formed is placed on the XY stage 101 so as to cover the substrate 10 on which the Ge thin film 20a to which Sn is added is formed. Pour pure water 102 into the water. With pure water 102 flowing in this manner, laser light is pulse-irradiated from the laser light source 104 toward the Ge thin film 20 a to which Sn has been added through the quartz window 103.

(Experimental result)
Next, in the method for forming a semiconductor thin film according to the present embodiment, the results of experiments performed by changing the irradiation conditions of the laser light irradiated on the Ge thin film 20a to which Sn is added, the Sn composition, and the like will be described. 3, 4, and 5 are experimental results when the laser beam is irradiated with pulses in pure water as shown in FIG. 2.

  First, the influence of Sn added to the Ge thin film will be described with reference to FIG. FIG. 3 shows the relationship between the fluence (laser fluence) of the laser beam irradiated with pulses to the Ge thin film 20a doped with Sn and the crystallization rate. The crystallization rate is a value calculated by separating the spectrum obtained by microscopic Raman spectroscopy into an amorphous component and a crystal component and then comparing the area ratio.

As shown in FIG. 3, the laser fluence is high for both the Ge thin film with no Sn added (without Sn) and the Ge thin film with 2 at% Sn added (Sn: containing 2 at%). Then, the crystallization rate is also high. In the case where Sn is not added to the Ge thin film (no Sn content), the crystallization rate rises to 0.85 at a laser fluence of 85 mJ / cm ² . However, when the laser fluence exceeds this value, Ge aggregation occurs and the crystallization rate does not reach 1.0.

In contrast, those Sn to Ge thin film is added 2at% (Sn: 2at% content), the in the laser fluence 300mJ from 190mJ / cm ² / cm ^2, and has a crystallization ratio 1.0 .

  That is, by adding Sn to the Ge thin film, damage to the thin film by laser irradiation can be suppressed, and the upper limit of the laser fluence can be increased. Thus, by increasing the laser fluence, Crystallization is promoted. The damage to the thin film due to laser irradiation is, for example, a state where Ge is aggregated and the form as a film is not maintained.

  As will be described later, in both cases where the laser light is irradiated in the air atmosphere and in the pure water atmosphere, the crystallization is promoted by adding Sn to the Ge thin film. Yes.

  FIG. 4 shows the result of examining the relationship between the laser fluence and the polycrystalline crystal grain size in the Ge thin film 20p to which Sn is added in the case where Sn is added to the Ge thin film (Sn: 2 at% contained). Is shown. The crystal grain size is calculated by an electron backscatter diffraction (EBSD) method. By increasing the laser fluence, the crystal grain size is increased about 100 times from about 0.01 μm to about 1 μm. This is because the laser fluence of the laser beam irradiated with pulses can be increased by adding Sn to the Ge thin film.

  FIG. 5 shows the results of investigating the relationship between the laser fluence and the Sn content contained in the polycrystal for the different contents of Sn added to the Ge thin film. Specifically, the sample is a Ge thin film with Sn added at 2 at% (Sn: 2 at% contained), a Ge thin film with Sn added at 5 at% (Sn: 5 at% contained), a Ge thin film What added 10 at% Sn (Sn: containing 10 at%) was produced. These were obtained as a result of pulse irradiation of laser light to these prepared Ge thin films to which Sn was added. The composition of Sn contained in the polycrystal was calculated from the amount of change in the peak position of the Ge—Ge bond obtained by microscopic Raman spectroscopy. When all of the manufactured Ge thin films to which Sn is added are irradiated with a laser beam having a high laser fluence, the composition of Sn contained in the polycrystal approaches about 2 at%. This is considered to be due to the fact that the solid solubility limit of Sn in Ge is 2 to 3 at%. Further, based on FIG. 5, the composition of Sn contained in the polycrystal can be adjusted to a desired composition by adjusting the amount of Sn added to the Ge thin film and the laser fluence.

  FIG. 6 shows a change in the crystallization state when a Ge thin film doped with Sn is pulsed with laser light in an air atmosphere. FIG. 7 shows changes in the crystallization state when a Ge thin film doped with Sn is irradiated with a laser beam in a pure water atmosphere. 6 and 7, symbol a indicates an amorphous state, symbol ○ indicates a crystallization state, that is, a polycrystalline state, and symbol x indicates damage caused by laser irradiation. It shows that. In both the air atmosphere and the pure water atmosphere, the addition of Sn can increase the laser fluence that causes laser damage, so that crystallization can be promoted.

  The inventors have confirmed that by setting the Sn composition to 0.1 at% or more, the laser fluence that causes damage due to laser irradiation can be increased. Moreover, if Sn composition is 20 at% or less, it has confirmed that it becomes a eutectic system, without segregating Sn in a thin film. That is, by adding Sn at 0.1 at% or more and 20 at% or less to the Ge thin film, it is possible to widen the margin of the laser fluence of the laser light to be pulsed, and the laser light is pulsed at the optimum laser fluence. be able to. Thereby, it becomes possible to perform the optimal annealing.

As shown in FIG. 6, when laser light irradiation is performed in an air atmosphere, the upper limit of the laser fluence is about 200 mJ / cm ² . In contrast, as shown in FIG. 7, when laser light irradiation is performed in an air atmosphere, the upper limit of the laser fluence can be increased to about 300 mJ / cm ² .

Next, a description will be given of the results of measuring the surface roughness with an atomic force microscope after pulsed laser light irradiation in an air atmosphere and pure water atmosphere. As a result, the surface roughness when the laser beam was pulse-irradiated with a laser fluence of 150 mJ / cm ² in an air atmosphere was about 30 nm. On the other hand, the surface roughness when the laser beam was pulse-irradiated with a laser fluence of 300 mJ / cm ² in a pure water atmosphere was about 10 nm. That is, the surface roughness can be made smaller when the laser beam is pulse-irradiated in a pure water atmosphere than when the laser beam is pulse-irradiated in the air atmosphere.

  Therefore, when laser light is pulse-irradiated in a pure water atmosphere, damage caused by laser light irradiation can be suppressed, flatness is high, and the crystallization rate is higher than when laser light is pulse-irradiated in the air atmosphere. High film thickness can be formed. Therefore, in the present embodiment, the atmosphere when irradiating the laser light is preferably a pure water atmosphere rather than an air atmosphere. As described above, a high-quality semiconductor thin film excellent in surface flatness and crystallinity can be obtained by irradiating a laser beam in a pure water atmosphere.

  Further, in this embodiment, since the laser beam is irradiated with pulses, only the Ge thin film to which Sn is added can be instantaneously heated. Therefore, it is possible to crystallize the Ge thin film to which Sn is added without almost transmitting the influence of heat generated by the pulsed laser beam to the substrate 10 or the like. For this reason, the board | substrate 10 can use what was formed with the resin material containing either silica glass, PEN, PET, PC, PI, etc. besides silicon | silicone. Silica glass and the above-described resin materials are transparent in the visible light region, and thus can be used for applications such as displays. Since these materials are vulnerable to heat, a thermal annealing furnace or the like cannot be used for crystallization of the Ge thin film when annealing, but annealing is performed in the present embodiment. Is possible.

  The substrate 10 may include either a semiconductor integrated circuit or a semiconductor element. For example, the substrate 10 may be a substrate in which a semiconductor integrated circuit or a semiconductor element is formed on a silicon substrate. In semiconductor integrated circuits and semiconductor elements, Al and solder materials are sometimes used for wiring and electrodes, and these materials have a low melting point, so a thermal annealing furnace or the like is used to crystallize a Ge thin film. This is not preferable.

  In addition, the film thickness of the Ge thin film 20a to which Sn is added as described above is preferably 10 nm or more and 1 μm or less, and more preferably 20 nm or more and 200 nm or less. This is because when the film thickness of the Ge thin film 20a to which Sn is added is thin, for example, when the film thickness is less than 10 nm, crystallization hardly occurs and the crystallized state is not promoted. Further, when the film thickness a of the Ge thin film 20 to which Sn is added is large, for example, when the film thickness exceeds 1 μm, only the vicinity of the surface of the thin film is crystallized, and the amorphous state is left in the deep region of the thin film. This is because sufficient semiconductor characteristics cannot be obtained.

  In addition, the wavelength of the laser light that is pulse-irradiated to the Ge thin film 20a to which Sn is added is preferably about 193 nm or more and about 532 nm or less. When the pulsed laser beam has a wavelength shorter than about 193 nm, the irradiated laser beam is absorbed by pure water, so that the Ge thin film 20a to which Sn is added is not sufficiently irradiated. Unable to anneal. Further, when the wavelength of the laser beam irradiated with the pulse is longer than about 532 nm, the efficiency of crystallization in the light irradiation annealing is lowered.

In the above description, the case of a Ge thin film doped with Sn has been described. However, the present invention can also be applied to Si, which is the same group IV semiconductor as Ge. That is, as long as Sn is added, any of Ge, Si, SiGe mixture in which Si and Ge are mixed, and the like can be applied. In other words, the effect in the present embodiment is an effect obtained in a semiconductor where 0.001 ≦ 1-xy ≦ 0.2 when described as Si _x Ge _y Sn _1-xy .

  As described above, in the method for forming a semiconductor thin film in the present embodiment, since laser light is irradiated with pulses, thermal energy can be instantaneously applied only to the formed thin film. In addition, since Sn is added to a thin film of Ge, Si, SiGe or the like in an amount of 0.1 at% or more and 20 at% or less, crystallization can be promoted while preventing aggregation in the thin film.

  Therefore, the substrate is not limited to the substrate on which the semiconductor thin film is formed, and a high-quality group IV semiconductor thin film such as Ge, Si, or SiGe having high carrier mobility and excellent surface flatness can be obtained. .

  In the method for forming a semiconductor thin film in this embodiment, when laser light is pulse-irradiated in a pure water atmosphere, the heat generated by the pulsed laser light is thermally diffused from the surface of the thin film toward the pure water. To do. Thereby, since more thermal energy can be given to a thin film, crystallization of a semiconductor thin film can be promoted further.

  The above description is intended to be illustrative only and not limiting. Thus, it will be apparent to one skilled in the art that modifications may be made to the embodiments of the present disclosure without departing from the scope of the appended claims.

  Terms used throughout this specification and the appended claims should be construed as "non-limiting" terms. For example, the terms “include” or “included” should be interpreted as “not limited to those described as included”. The term “comprising” should be interpreted as “not limited to what is described as having”. Also, the indefinite article “a” or “an” in the specification and the appended claims should be interpreted to mean “at least one” or “one or more”.

Claims (10)

Depositing a thin film containing any of Ge, Si, and a SiGe mixture on the substrate and Sn of 0.1 at% or more and 20 at% or less;
Irradiating the thin film with pulsed laser light. The method of forming a semiconductor thin film according to claim 1, wherein the thin film is changed from an amorphous state to a polycrystalline state by irradiating the thin film with the pulsed laser light. The method for forming a semiconductor thin film according to claim 1, wherein the substrate is a glass substrate. The method for forming a semiconductor thin film according to claim 2, wherein the substrate is a glass substrate. The method for forming a semiconductor thin film according to claim 1, wherein the substrate includes any one of a semiconductor integrated circuit and a semiconductor element. The method for forming a semiconductor thin film according to claim 2, wherein the substrate includes any one of a semiconductor integrated circuit and a semiconductor element. The method for forming a semiconductor thin film according to claim 1, wherein the substrate includes any one of polyethylene naphthalate, polyethylene terephthalate, polyimide, and polycarbonate. The method for forming a semiconductor thin film according to claim 2, wherein the substrate includes any one of polyethylene naphthalate, polyethylene terephthalate, polyimide, and polycarbonate. The method for forming a semiconductor thin film according to claim 1, wherein the irradiation of the pulsed laser light onto the thin film is performed in pure water. The method for forming a semiconductor thin film according to claim 1, wherein a wavelength of the pulse laser beam is about 193 nm or more and about 532 nm or less.

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